A DC-DC converter may be used when circuitry in an integrated circuit needs a special power supply voltage. The DC-DC converter uses an inductor and transistor switches to connect and disconnect the inductor temporarily to and from different power supply terminals, in order to generate the special supply voltage. The transistor switches of the DC-DC converter may be integrated in an integrated circuit, together with control circuits of the DC-DC converter. Not all circuitry of the DC-DC converter needs to be integrated. Often the inductors of the DC-DC converter are discrete components outside the integrated circuit.
U.S. Pat. No. 6,028,755 discloses an example of a DC-DC converter. This converter comprises a first transistor switch coupled between one terminal of an inductor and ground and a second transistor switch coupled between said one terminal and a supply input.
In addition, the converter comprises a control circuit, with outputs coupled to the gates of the transistor switches. This control circuit regulates the output voltage, by controlling the time points at which the switches are switched on and/off. In addition the control circuit provides for over-voltage protection of capacitors of the DC-DC converter.
Circuits are provided that compare divided down versions of the input and output voltages with reference voltages and make the transistor switches conductive, to short circuit the power supply in the case of an over-voltage.
U.S. Pat. No. 4,672,303 similarly shows a DC-DC converter with an over-voltage protection circuit. Herein the divided down version of the output voltage is compared with a reference voltage and used to short circuit the power supply in the case of an overvoltage.
The transistor switches of a DC-DC converter have to carry considerable currents. As a result, transistor switches must be used that take up considerable circuit area in the integrated circuit. This problem is exacerbated by the fact that the transistor switches are connected to output terminals of the integrated circuit, which means that special, larger area transistors must be used in order to protect against damage by electrostatic discharge (ESD) during transport and handling of the integrated circuit, before it is mounted in a circuit.